Sizing radiators for rooms

[Joshua Graham]

Hi, I had an installer fit an ASHP to my existing heating system. They advised i should upgrade my radiators at the time as it was about 30 years old and micro bore etc. I was a bit strapped for cash at the time of installation so I had no choice but to refuse and come back at a later date to fit new radiator system. As a result I have left my self unsure as to how to scale the radiators for the rooms and what BTU they need to be. I was hoping to run the ASHP as low as possible around 35-40 degrees to reduce long term strain on the system, so have no issue over sizing the radiators. How would I calculate the sizes? I was left with these documents and I am unsure if they are what I need to calculate this out. Also attached is a detailed floor plan of the area needing heated in case that helps. Thanks in advance for any replies, help and support offered.

Mike

 

[JohnMo]

You use the power in watts to size each room radiator, so room 1 needs 618W output from radiator.

 

Now you need to convert the radiator size from manufacturer data to your chosen flow temp. There is a calculation on here somewhere so do Google search on buildhub.

 

You need to look at the pipe sizes then as most of the micro bore may need replacing(?).

 

Did they install a buffer?

[Joshua Graham]

13 minutes ago, JohnMo said:

You use the power in watts to size each room radiator, so room 1 needs 618W output from radiator.

 

Now you need to convert the radiator size from manufacturer data to your chosen flow temp. There is a calculation on here somewhere so do Google search on buildhub.

 

You need to look at the pipe sizes then as most of the micro bore may need replacing(?).

 

Did they install a buffer?

That is great thanks. I have replaced the micro bore with a manifold system and 15mm pex pipe. There is a tank if that is what you mean by a buffer (sorry for my ignorance!) built into the valiant internal unit. Should i install an expansion vessel on the radiator loop also?

Thanks for your reply, I will lookup the calculation tool.

[Nickfromwales]

12 minutes ago, Joshua Graham said:

That is great thanks. I have replaced the micro bore with a manifold system and 15mm pex pipe. There is a tank if that is what you mean by a buffer (sorry for my ignorance!) built into the valiant internal unit. Should i install an expansion vessel on the radiator loop also?

Thanks for your reply, I will lookup the calculation tool.

The vessel inside the internal unit may just be an expansion vessel (EV). 
 

A buffer tank is a stand alone cylinder which is in addition to your EV’s and hot water cylinder.

 

Have a look at the manufacturer’s installation guidelines, it should tell you there what system volume the OEM (factory) EV can cope with, so only add more if the upsized rads increase the water volume in excess of its current capacity.

[Joshua Graham]

Gosh, I have to admit, I feel more confused then before. Thanks everyone for the input. I am probably going to have to have a serious sit-down and look into this, or if there are suggestions on who to hire to help with this?

[Joshua Graham]

I am very confused, some sources say 2.5 times the BTU (I would imagine watts would work also) for ASHP but this just sounds a bit loosey-goosey advice and could lead to cold rooms. Is this advice sound? It doesn't seem to take into account that I would like to run the system at lower temperatures.

[Joshua Graham]

Ok, I will have to take a look at the manual see what the case is.

Edited Monday at 11:19 by Joshua Graham